The present invention relates to a process for producing a wound dressing delivery system.
Recent approaches to the production of wound dressings focus on the concept of moist wound healing. Experimental work indicates that the regrowth of epithelial tissue on a wound occurs more rapidly under moist conditions. The environment which promotes such tissue regrowth depends on the adherence, the bacterial barrier, the oxygen transportation, and the water vapor transportation of the wound dressing.
Adherent wound dressings which, in their simplest form, consist of an oxygen and moisture vapor permeable film which is adhered to the wound site by an adhesive of similar permeability, have been designed. These dressings are both occlusive and permit the free flow of oxygen and other gases through the wound dressing. An important consideration in designing the films used in these dressings is the level of oxygen and moisture transmission through the layers of an adherent wound dressing. The advantages of a high percentage of oxygen transmission through the wound dressing are that the oxygen is made available to both the white blood cells in the wound and also to the newly-grown tissue on the wound surface for the purpose of maintaining functional viability through aerobic metabolism. Moisture permeability permits the wound to breathe and sweat normally.
An example of an adhesive backed polyurethane occlusive dressing is disclosed in U.S. Pat. No. 3,645,835 to Hodgson. The dressing comprises a backing material which is an unreinforced thermoplastic polyurethane film, having a pressure-sensitive adhesive on one face for binding the film to the wound site. Suitable thermoplastic polyurethane film is made by extrusion or by solvent casting. The adhesive may be applied to the polyurethane film in solution, as an aqueous dispersion, as a hot melt, or by a transfer process. Under the convenient transfer process, the adhesive solution is spread on release-coated paper, and almost dried before contacting the polyurethane film under sufficient pressure to ensure good contact. The release paper is then removed. The dressing is water vapor permeable but not liquid water permeable. The dressing has a moisture vapor transmission rate of at least 300 grams/square meter/24 hours/40.degree. C./80% R.H.
Other medical dressings include that disclosed in U.S. Pat. No. 3,426,754 to Bierenbaum et al. The dressing comprises a backing and a pressure-sensitive adhesive coating. The preferred backing is an olefin polymer. To prepare a suitable backing, the backing is extruded and then drawn to impart an open-celled structure and to reduce the apparent density. The open-celled structure permits maximum gas permeability. The adhesive may then be applied to the backing in any way which prevents adhesive penetration through the backing after the adhesive is dried.
U.S. Pat. No. 4,367,732 to Poulsen et al. discloses a skin barrier wherein a silicone release paper is overcoated with polyethylene, an elastic film, and an elastic adhesive. A silicone release paper may be optionally secured to the elastic adhesive. The elastic film and the elastic adhesive in combination function as the claimed skin barrier. The preferred elastic film is a polyurethane film. The elastic adhesive is a mixture of a crosslinked elastomer, a hydrocarbon tackifier resin, a polar plasticizer, an antioxidant, an oily extender, and a hydrocolloid. The support material and the optional silicone release paper are removed prior to use.
U.S. Pat. No. 4,516,571 to Buchan discloses a medical dressing which is filled with polyurethane gel and has walls formed from polyetherpolyamide block copolymer film. An adhesive may be coated on the body contacting surface of the film. The dressing has a water vapor transmission rate of greater than 300 grams/square meter/24 hours at 37.degree. C. at 100% to 10% relative humidity. The film may be formed into strips of the appropriate size, folded, and heat sealed along the sides to provide an envelope with an opening; the envelope may also be blow molded or vacuum formed. The polyurethane gel is then transferred to the polyetherpolyamide block copolymer envelope and the envelope is closed by heat sealing.
Understandably, the products, which result when the aforementioned properties are taken into consideration, are skin-like in appearance and in their physical characteristics. These properties make the products difficult to handle, particularly in large formats, during manufacturing. The present invention is directed to a process for manufacturing films useful as a wound dressing on a carrier sheet. In accordance with the present invention, the films are extrusion coated onto a carrier sheet. This intermediate product may then be shipped to a manufacturer for application of an adhesive coating, which may be medicated, and an adhesive liner. The carrier sheet is then readily removed for packaging.